Phonograph pickup unit using magnetostrictive wire



May 31, 1949. s. R. RICH PHONOGRAPH PICKUP UNIT USING MAGNETOSTRICTIVEWIRE Filed Oct. 25, 1945 M m wk W F B 5 2 a 6 W5 L m 1 m w F r\\ F 5v: 2.l O B .1 q 2 3 F ///,,,\V U \\\.\\N\ m :P F. 3 WM MS l. 4 7 m n F F F.

Patented May 31, 1949 PHONOGRAPH PICKUP UNIT USING MAGNETOSTRICTIV EWIRE i Stanley R. Rich, Cambridge, Mass.

Application October 25, 1945, Serial No. 624,362

8 Claims.

The present invention relates to a phonoraph pick-up unit for convertingmechanical vibrations into corresponding electric vibrations.

The present invention is particularly useful in reproduction of soundfrom phonograph records, but may of course be applicable to any othertype of energy conversion between mechanical vibrations andcorresponding electric current.

There are many various units in current use for reproduction of soundrecorded on phonograph records and for cutting records from sound. Someof these are comparatively large and heavy, particularly the partsentering into the vibrating system, with a general result that whilevibrations of lower frequencies are faithfully reproduced, nevertheless,the presence of the large vibrating masses interferes substantially withthe faithful and full reproduction of higher frequencies. A furtherdifficulty has been found in obtaining sufficient sensitivity andresponse with pick-up units now generally used.

In the present invention as applied to reproducing of sound, thevibrating element in the unit is hardly more than the stylus itself.Full and efficient use is made of the vibrational stresses in theportion of the unit which is actuated by the stylus. It will also benoted that the coupling between the vibrating element and the pick-upcoil is extremely close and made to function in such a way that thepotential generated in the coil is additive for the pick-up operationand arranged to balance out extraneous electrical or mechanicaldisturbances. The phonograph unit of the present invention is furtherextremely simple to manufacture, requires substantially no adjustmentand is durable, rugged and will not be injured even with extremely roughtreatment. No fine or accurate adjustment need be made to this device,and since no crystal elements are employed, dropping the unit on thefloor or the like will not injure it.

The present invention will be more fully explained in connection withthe embodiment described in the specification below when read inconnection with the drawings, in which- Figure 1 shows an elevation ofthe phonograph pick-up unit.

Figure 2 shows an end view of the unit seen in Figure l as viewed fromthe right of that figure.

Figure 3 shows a section taken on the line 33 of Figure 1.

Figure 4 shows a further modified form of the unit of Figure 1, theneedle being positioned in a different direction.

Figure 5 shows an elevation as seen when looking at the lower end ofFigure 4.

Figure 6 shows an end view of Figure 4 as Viewed from the right of thatfigure, and,

Figure 7 shows a further modified form of Figure 1.

In the arrangement of Figures 1, 2 and 3, the unit comprises a pair ofC-shaped magnets, I and 2, which may be of the alloy material such asAlnico, comprising aluminum, nickel and cobalt, or Cunico comprisingcopper, nickel and cobalt or any other powerful permanent magnetelements.

The two C-shaped pieces may be fittted face I: to face and are heldtogether at convenient places,

as for instance at the corners by the bolts 4, 4, passing through thetwo pieces.

In the present construction it is preferable to assemble the two piecesI and 2 together and then to drill at the joining line of each armelements of the c magnets, holes 5, 5 aligned together, or if thesurfaces are too hard to drill, semi-circular holes may be ground ineach edge surface. These holes may be sufficiently large for a slidingfit to accommodate a magnetostrictive wire 6, or if additional tensionon the wire is desired, the two halves of the G magnet may serve toclamp the wire firmly, which passes through the holes 5, 5, adjacent theend of the elements or prongs of the C. The wire 6 terminates at eitherend in hooked or angle elements I and 8 with small inwardly extendingterminal pieces 9 and In which are at angles to the portion 1 and 8 andlay over the faces of the magnet.

As indicated more clearly in Figures 2 and 3, the end angle elements Iand 8 are twisted, so so that the wire at one end is given a torsionalstress in one direction of rotation of the wire, and the other end isgiven a torsional stress in the other direction of rotation of the wire.

As indicated in Figures 1 and 2, the wire 6 at its right end is twistedto bring the end 9 on the forward face of the magnet I, while the end 8is twisted to bring the end N) of the wire at the forward face of themagnet 2. The wire is therefore given a torsional twist whichapproximates in the arrangement of Figures 1 and 2 about 90. The wiremay be given a greater or less stwist, angle of twist not being criticalsince considerable leeway is permitted in the present design. It isdesirable to provide however a twist of such a magnitude, taking intoconsideration the length of the wire, that the magnetostrictive forcesemployed may be used most efiiciently. The torsional stress so exertedon the wire 6 will place the fibers of the wire longitudinally intension and will at the same time provide shearing forces, both of whichwill tend to increase the magnetostrictive variations brought aboutthrough the operation of the device.

A coil of fine wire H is wound about the wire 6 and serves to pick upthe flux variations produced by the mechanical twisting force acting onthe wire 6 at the point of the wire 8 where the stylus is. Between thetwo ends, and at the midpoint preferably, the stylus I2 is attached bywelding, soldering or any other suitable manner. The stylus may be around or flat element and carries at its end a jewelled point 13 such assapphire or diamond or any other similar type of point which will wearsubstantially indefinitely or for a very long time when used onphonograph records. The point may be removable by having a screwthreaded connection to the stylus. The coil or wire need not be ultrafine but may be of No. 40 and Wound in one or more layers with thedesired resistance. The coils, one on either side of the stylus, will beconnected to an electrical system, such as an amplifier with propermatchmg by means of a suitable transformer. The coils II are connectedin such a manner that current flows in opposite directions of rotationover the two halves of the wire 6, that is on one half andcounterclockwise on the other half.

In the arrangement in Figure 1 it is assumed that the pick-up unit willmove in the direction or the arrow A over the phonograph record, thepoint l3 following in the record groove substantially in the samedirection with the stylus I2 vibrating perpendicularly to the plane ofthe paper as viewed in Figure 1. This action will produce torsionalvibration of the wire 6, which one half will tend to relieve the tensionin the longitudinal direction and reduce the magnitude of the shearingforces. In the other half of the wire 6, the opposite action will takeplace. The reluctance of the first mentioned half of the wire '6 willdecrease and that of the second mentioned h'al'f wi'll increase. Thechange in the first half will be to reduce the flux, while in the otherhalf 'to increase the flux so that by winding the coils in the twohalves in opposite directions, the direction of the generated potentialwill be additive.

I have found that the lines of force or flux on account of this actionleaves the magnetostrictive wire along its length as the torsion isvaried. As the reluctance increases in a portion of the wire, more linesof force leave in that portion, and when the reluctance decreases, lessflux leaves the wire so that while the reluctance of the whole wire pathmay remain the same within the limits of operation, the flux in eachhalf of the wire changes in opposite directions to produce additiveelectromotive force in oppositely wound coils. A 7 It will be notedfurther in the arrangement of Figures 1, 2 and 3, that the operation isone of torsion of the wire 6, so that the wire 6 occupies the sameposition throughout its torsional vibrations. There is no substantialmotion of the wire as a whole. As a mechanical protection for the wire,and as a clamping means, if desired, a support It in the shape of awedge, may be extended to a point adjacent the center of the wire wherethe stylus is attached to prevent excessive mechanical forces notencountered in the operation of the wire from injuring it. This wedge Mmay be retained in a recess between the magnet sections I 'and 2 asindicated at M.

For so called hill and dale record, the same arrangement indicated inFigures 1, 2 and 3, may be used. The only change necessary in such anarrangement is that the stylus l2 would be positioned to providetorsional vibrations when drawn over the hill and dale record. As viewedin Figures 2 or 3, the stylus under these conditions would be inclinedto the right or left instead of straight down.

While it is preferable and of simple construction to have the wire t ina free sliding fit in the holes 5, nevertheless it may be desirable, asmentioned above, to obtain longitudinal tension, to clamp the wire 8rigidly in place between the two magnet elements l and 2. This of coursebe accomplished by making the hole 5 smaller so that the two magnets land 2 when pressed together will act to clamp the wire in the groove. Insuch a case the end sections or the wire 1, 9, and 8, It, may beeliminated after the desired torsional stress has been applied to thewire 6.

In the arrangement of l 'gures e, 5 and 6, the device substanti .e as ofFig ure 1 and like eiements are referred to by the same numbers.

In these figures the stylus 3t is directed at an angle with the plane ofthe device which is drawn over the record plate in the direction of thearrow B. The vibrations of the stylus due to the record is assumed to beperpendicular to the plane of the paper.

In the arrangement of Figures 4, 5 and 6, a pair of formed coils 3| and32 may be mployed. These may be slipped over the wire ii which isarranged and constructed in the same Way as in Figures 1, 2 and 3.

The guard element corresponds substantially to that of the element i l,with the exception that it extends over the wire E at the side of t".midsection as indicated at the end 35 in Figures 4 and 5 to protect thewire The operation of he mod. mien of Figures 4, 5 and 6, issubstantially the same as that of Figures 1, 2 and 3. The action in thetwo coils '31 and 32 is made to be additive by suitable connection.

In the arrangement indicated in Figure 7, the par-ts are substantiallythe same as in Figure 1, and to that extent they are similarly numbered.The difference in structure resides principally in the use of a balancedmagnetic circuit in which the magnet has a central arm til, the magneticpotential of which is neutral, or half way between the end arms 42 and23. A coll li is wound around the central section lEl which extends toa, point mid-way between the ends of the wire 6. Under normal conditionswhen no torsional vibration is impressed upon the wire, the reluctanceof both halves of the wire ii is th same, and the flux passing through.the central section 6Z3, remains balanced. When the torsional stresseson one half of the wire 6 are released, the reluctance of this halfincreases and that of the other half decreases, because of increasedtorsional stresses. This changes the balance in the section it andprovides an increasing in magnetic flux which induces the voltage in thecoil M which is impressed upon the electrical phoncgraph or amplifiercircuit.

The device as indicated above will also operate in the reverse manner.If current is impressed on the coils II or H, the flux in the wire 6will change and the mechanical forces will be altered 'or varied in thewire to produce motion which will vibrate the stylus for the purposes ofcutting a sound groove or producing a sound film.

Having now described my invention, I claim:

1, A phonograph pick-up device comprising a permanent magnet of highflux retentivity, providing two opposing pole elements, amagnetostrictive wire bridging said pole elements and supported thereby,means maintaining said magnetostrictive wire in torsion between the poleelements the torsional stresses acting in the same direction along itsentire length, a stylus attached to said magnetostrictive wire in freeequilibrium and extending from said magnetostrictive wire at the midsection thereof and a coil wound about said magnetostrictive wire onboth sides of said stylus for converting the magnetic flux variationsproduced by said magnetostrictive wire to eleetro motive force.

2. A phonograph pick-up device, comprising a C-shaped permanent magnetformed of two 0- shaped sections supported together in face to facerelation, a magnetostrictive wire bridging the pole elements of saidmagnet and supported between the C-shaped sections, means providing andsustaining torsional stress in said magnetostrictive wire between thesupported portions thereof, a free stylus extending from saidmagnetostrictive wire between its supported portions and coil means forconverting the magnetic flux variations produced by saidmagnetostrictive wire to electromotive force.

3. A phonograph pick-up device, comprising a C-shaped permanent magnetformed of two C- shaped sections supported together in face to facerelation, a magnetostrictive wire bridgingthe pole elements of saidmagnet and supported between the C-shaped sections, means providingtorsional stress in said magnetostrictive wire between the supportedportions thereof, a. free stylus extending from saidmagnetostrictivewire between its supported portions and coil means wound about saidmagnetostrictive wire for converting the magnet flux variations producedby said magnetostrictive wire to electromotive force.

4. A phonograph pick-up device comprising a permanent C-shaped magnetformed in two similar C-shaped sections, means retaining said C-shapedsections together, a magnetostrictive wire extending between the polesof said C-shaped magnets, said magnetostrictive wire being supportedbetween the faces of said C-shaped sections, means providing a torsionalstress on said magnetostrictive wire, said means comprising end sectionsof the wire twisted in opposite directions and having end elements lyingover the pole elements of the G-shaped magnets, a free stylus attachedto said magnetostrictive wire between its end support and coil meanswound around said magnetostrictive wire for converting the magnetic fluxvariations produced by said magnetostrictive wire to electromotiveforce.

5. A phonograph pick up device comprising a magnetostrictive wire, meanssupporting said magnetostrictive wire at its ends and placing the wirein torsion between the supporting ends, the torsion acting in oppositeangular directions at its ends as viewed from either end, a stylus freeat one end and attached at its other end to the magnetostrictive wire ata point between the supported ends of the magnetostrictive wire, meansfor polarizing said wire with magnetic flux longitudinally of the wire,and coil means for converting magnetic flux variations produced by saidwire to electromotive force.

6. A phonograph pick up device comprising a magnetostrictive wire, meanssupporting said wire at two spaced points in alignment with said Wire,means providing a torsional stress acting in the same angular directionalong the wire between its supported points, a free stylus attached atone end to said magnetostrictive wire between said two points ofsupport, means for polarizing said wire with magnetic flux, and coilmeans surrounding the wire for converting the magnetic flux variationsinto electromotive force.

7. A phonograph pick up device comprising a magnetostrictive wire, meanssupporting said magnetostrictive wire at its ends and placing the wirein torsion between the supporting ends, means providing a torsionalstress acting in the same angular direction along the wire between itssupported ends, a free stylus attached at one end to saidmagnetostrictive wire, said stylus adapted to vibrate to relieve thetorsional stress in the magnetostrictive wire at one side of themid-point thereof and increase it at its other side, means forpolarizing said wire with magnetic flux, and coil means for convertingthe magnetic flux variations produced in the magnetostrictive wire toelectromotive force.

8, A phonograph pick up device comprising a magnetostrictive wire, meanssupporting said wire at two spaced points in alignment with said wire,means providing a torsional stress acting in the same angular directionalong the wire between its supported points, a free stylus attached atone end to said magnetostrictive wire substantially at the midpointthereof, means for polarizing said wire with magnetic flux, and coilmeans positioned at each side of said midpoint of the magnetostrictivewire and wound about it for converting magnetic flux variations thereinto electromotive force, said coil means being wound to make the effectof said variations additive in producing said electric force.

STANLEY R. RICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 351,905 Eichemeyer Nov. 2, 18861,821,836 Hull Sept. 1, 1931 1,882,400 Pierce Oct. 11, 1932 2,343,352Mallina May 9, 1944 FOREIGN PATENTS Number Country Date 513,062 GermanyJan. 25, 1928

